Whew, $200 is really something and would be a bit much for me as well.
I’m currently preparing to learn shaders in Unity myself. Here’s what I found. (Note that I haven’t read them yet, but I added them to my list because I either know other things by the authors or they just seem very promising.)
Apart from the first one, everything in this list is free. PluralSight is pretty awesome though!
- Introduction to Scripting Shaders in Unity by Joshua Kinney ($29/month for the PluralSight subscription)
- Unite Europe 2016 - A Crash Course to Writing Custom Unity Shaders! by Andy Touch
- Unity 5 Shader Programming by digitalerr0r
- This 15 part (with more coming, probably) series on Rendering (actually mostly about shaders ;)) by Catlike Coding
- A lot of more specific shader topics and examples by Alan Zucconi
- The newer shader articles by Kyle Halladay look interesting, especially The Basics of Fresnel Shading, Coloring Shadows, Getting Started With Compute Shaders In Unity, A Burning Paper Shader, Screen Space Distortion and a Sci-fi Shield Effect by Kyle Halladay, Distorting Object Shapes in Screen Space, A Pencil Sketch Effect and Fixeds, Floats and a Block Damage Effect
- Lots of example shaders and a few tutorials by Shaders Laboratory on YouTube
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The Cg Programming/Unity wiki has quite some tutorials (and a lot in the “missing” section just to make you aware of what you are missing out
) - Compute And Geometry Shader Tutorial by NemoKradXNA